Currents vs larval biology: The biology matters

Dr Shima at Victoria's Marine Lab reports that fish larvae can actively control their distribution in the ocean - not just vertically - and that where they grow up has a large effect on their chances of survival. I can't wait to see the publication(s), since these ideas are both counter to much prevailing dogma regarding marine larvae.

Larvae are small and generally believed to be weak swimmers with little to no capacity to counter the strong ocean currents. Fish larvae are more proficient swimmers than their invertebrate counterparts, but are still quite weak especially during early stages. Yet, Dr. Shima reports that fish larvae are preferentially found along the coast, rather than swept out to sea as current flow would predict. It is not clear how the larvae are accomplishing this feat, but it highlights the importance of considering biology in estimates of larval dispersal and population connectivity.

Although it really shouldn't be, the importance of WHERE larvae grow up may be even more revolutionary for considering population connectivity - which is in essence a network of lines connecting larval birth places with the location where they spend adulthood. There is no consideration of the planktonic trajectory in between - just beginning and end.  However, more and more experimental evidence and now field observations support the idea that larval quality which is a function of its experience in the water column has a profound effect on which larvae are successful once they settle. Dr Shima suggests that Wellington Harbor may act as a type of nursery habitat, increasing the success of triplefin larvae. For some (many?) species, it may not be enough that they simply get there, but that the larvae also experienced favorable environmental conditions for rapid growth and development to facilitate survival to adulthood.

It is likely these biological factors that can account for differences between observed or actual population connectivity and the output of oceanographic models.


Reference: More than chance determines future for baby fish, Voxy.co.nz